1. Field of the Invention
The present invention relates to an optical scanning device which scans the surface of photosensitive body by deflecting laser light towards a predetermined direction at a constant speed, and to an image forming apparatus utilizing the same.
2. Description of the Related Art
A conventional technique has been known relating to an optical scanning device for laser printers and copiers in which a laser beam emitted from a light source is deflected by rotation of a polygon mirror for scanning, a portion of the laser beam having passed through an imaging lens is reflected by a fold mirror, a BD (Beam Detect) sensor sends out a detection signal when it receives the portion of the laser beam at its light receiving surface, and timing of the initiation of writing to a photosensitive body is provided based on the detection signal.
According to the conventional art, for example, the fold mirror is composed of a concave mirror in order to guide a light beam (laser beam) having passed through a scan lens (imaging lens) to a BD sensor. The concave mirror is attached to an L-shaped mounting bracket, and an adjusting screw comes into contact with the back side of the concave mirror, allowing adjustment of slope of the concave mirror by changing the protruding amount of the screw.
However, the above conventional art has problems of not only an increased cost due to necessity of an extra member for attaching a concave mirror such as the L-shaped mounting bracket, but also of difficulties in assembly such that the detection accuracy of a BD sensor may be affected due to damages on the surface of the concave mirror caused by contact between the member and the mirror upon mounting.
When the concave mirror is attached so as to make an angle as big as possible between a laser beam received by a light receiving surface of a BD sensor previously reflected by the concave mirror and a laser beam thereafter initiating scanning the surface of a photosensitive body previously deflected by a polygon mirror, it is necessary to increase the duration for deflecting a laser beam for scanning on one surface of the polygon mirror, causing a problem such that the optical scanning device may be enlarged.